DE102017003876A1 - Wind energy plant with converter connected via a connecting line - Google Patents

Abstract

The invention relates to a wind energy plant with a generator arranged in a nacelle and a converter connected via a connecting line. In particular, the inverter is arranged gondelfern and connected via a long connecting line to the generator in the nacelle. In order to improve the wind turbines so that the filters are less critical, are also provided with a synchronous two carriers for controlling the flow control valves, each with a cycle position, a relative position detector, which is adapted to determine the cycle position for both inverters and to determine their relative position to each other, and a Zyklenlageschieber, which cooperates with the relative position detector and is adapted to shift the cycle position of at least one of the inverters depending on the determined relative position.

Description

The invention relates to a wind energy plant with a generator arranged in a nacelle and a converter connected via a connecting line. In particular, the inverter is arranged gondelfern and connected via a long connecting line to the generator in the nacelle.

In modern wind turbines with inverter two fundamentally different types are known. One type provides for a common arrangement of generator and inverter in the nacelle. Here, either the generator and the inverter are locked together or connected to each other via a very short connection line. This brings the advantage of a short low-voltage connection with it. Furthermore, the arrangement is compact. However, the arrangement of the inverter in the nacelle is often unfavorable for structural reasons.

The other type provides a distributed arrangement of generator and inverter, the inverter is not located in the nacelle, but gondola remote in the tower or even at the base of the tower. This arrangement can book constructive advantages for themselves. First, the considerable weight of the inverter is not at the top of the head of the tower, but arranged further down. On the other hand, the connection line is now a pure low-voltage line, so that accordingly inside the tower compliance with the less stringent rules for dealing with low-voltage systems apply (unlike the much stricter regulations for handling medium voltage systems, as would otherwise be required) , This regulatory advantage is counteracted by the disadvantage that, due to the block-shaped voltages impressed by the converter, traveling waves can occur on the connecting line and then also in the generator winding in conjunction with parasitic capacitances, leading to overvoltages and resonances. These can lead to damage. It is therefore attempted to reduce it by voltage filters.

In practice, however, in wind turbines with inverters arranged remote from the gondola, the design of said filters often presents problems. Because they have to serve different goals. On the one hand, it is about limiting the edge steepness and keeping overvoltages low. Furthermore, the transient response should be damped as well as possible. All this should be achieved without producing large losses. These requirements are usually contrary in practice. The design of the filter is therefore difficult. Over the operating range, they are often not robust and / or have high losses.

The invention is based on the object to improve the wind turbines so that the filters are less critical.

The solution according to the invention lies in the features of the independent claims. Advantageous developments are the subject of the dependent claims.

In a wind turbine with a generator in a nacelle, which is driven by a wind rotor, a converter, which cooperates with the generator for generating electrical power, a connecting line between the generator in the nacelle and the inverter, which is preferably arranged away from the gondola, wherein the inverter a generator-side and a network-side inverter whose current valves are cyclically controlled by means of a switching frequency, the invention provides a synchronous with two inverters carrier for controlling the flow control valves, each with a cycle position,
a relative position detector, which is designed to determine the cycle position for both inverters and to determine their relative position to each other, and a Zyklenlageschieber, which cooperates with the relative position detector and is adapted to shift the cycle position of the inverter depending on the determined relative position.

By shifting the relative cycle position can thus be achieved a significant reduction of common mode voltages on the connecting line. This also reduces the excitation to oscillations and traveling waves accordingly. It has been found that with the measures according to the invention, a reduction of the voltage of the common mode oscillations by 2/3 can take place. Filter and voltage losses are significantly reduced - not least because of the quadratic relationship between voltage and power. The filters therefore no longer need to be designed as aggressive, and thus become more robust and have lower losses. This allows the use of simple, smaller filters. In addition, the losses are reduced.

The converter can be designed as a full converter (in particular for squirrel-cage asynchronous generators or synchronous generators) or as a partial converter (in particular for double-fed asynchronous generators).

Conveniently, the relative position detector is designed to drive the cycle shifter only when the relative position is outside of an interval. In this case, the limits of the interval are preferably determined dynamically.

Preferably, a selector is provided which dynamically selects with advantage which of the two inverters of the converter is shifted relative to its cycle position. The effect on only one of the two inverters allows a more direct control and avoids incidentally the risk of control oscillations by unwanted positive feedback. Conveniently, the selector is actuated load controlled. This can be controlled with advantage in such a way that, depending on a load dimension, that inverter is selected by the selector which has the lower load dimension. This has the advantage that the less loaded of the two inverters is used for the shift. Conveniently, the voltage at the two inverters can be provided as a load measure, in which case the inverter is selected by the selector, which has the lower voltage; Alternatively, a time parameter can also act as a load measure, for example an interval duration of an interval that is spanned between the minimum value and the maximum value, as will be explained in more detail below.

Advantageously, a phase sorting unit is provided, which with respect to the phases of the inverter to sort according to their amplitude. Expediently, such a transformation unit is provided for each of the two inverters. The transformation unit thus arranges the phases in terms of their amount and thus enables a simpler determination of the cycle situation. By means of an interval forming module, the interval can expediently be formed from the minimum and maximum phase.

Conveniently, a cross-comparison unit is provided which compares the position vectors of the two inverters with each other crosswise. By "crosswise" is meant here that a value for the middle phase of the one inverter is compared with values for the minimum and the maximum value of the other inverter. It is checked whether the average value is in the interval spanned by the minimum value and the maximum value. If this is the case, a corresponding signal is output to change the cycle position of the inverter whose values determine the limits of the interval. Thus, by shifting the cycles of this inverter, it is forced to satisfy the condition of falling in the interval. In this way, an overlapping operation of the two inverters is ensured. This is, as the invention has recognized, favorable for a reduction of the common-mode voltages.

The invention also extends to a corresponding inverter for wind turbines. Furthermore, the invention extends to a corresponding method.

For a more detailed description, reference is made to the above statements on the wind energy plant according to the invention.

• 1. eine schematische Ansicht einer Windenergieanlage gemäß einem Ausführungsbeispiel der Erfindung;
• 2. ein Schaltbild eines Umrichters;
• 3. Diagramme zu einem Ansteuersignal des Umrichters;
• 4. ein Blockschaltbild für eine Ansteuerung des Umrichters;
• 5. ein Blockschaltbild zu einem Phasensortierer;
• 6. ein Blockschaltbild zu einem Relativlage-Detektor;
• 7. ein Diagramm zu Zyklenlagen;
• 8. Diagramme zur Ansteuerung von Stromventilen mit und ohne Gleichtakt-Optimierung; und
• 9. Diagramme zur Ansteuerung von Stromventilen des Umrichters mit unterschiedlicher Spannung.

The invention will be explained below with reference to the accompanying drawings with reference to an embodiment. Show it:

• 1 , a schematic view of a wind turbine according to an embodiment of the invention;
• 2 , a circuit diagram of an inverter;
• 3 , Diagrams for a control signal of the inverter;
• 4 , a block diagram for driving the inverter;
• 5 , a block diagram of a phase sorter;
• 6 , a block diagram of a relative position detector;
• 7 , a diagram of cycles;
• 8th , Diagrams for the control of flow control valves with and without common mode optimization; and
• 9 , Diagrams for controlling the current valves of the inverter with different voltage.

For an explanation of an embodiment of the invention, reference will first be made 1 , It shows one in its entirety with the reference number 1 designated wind turbine according to an embodiment of the invention.

The wind turbine 1 includes a tower 10 , at the top of which a gondola 11 Is arranged pivotably in the azimuth direction. At one end of the gondola 11 is a wind rotor 12 rotatably arranged. He drives over a rotor shaft 13 one in the gondola 11 arranged generator 14 at. In the gondola 11 is also an operation control 2 provided, which the operation of the wind turbine 1 controlled throughout.

At the foot of the tower 10 is an inverter 3 connected. It can be designed as a full converter or as a partial converter. The following explanation is based on the example of the embodiment as a full converter, wherein the generator 14 is designed as a squirrel cage asynchronous generator (other embodiments are also possible). The inverter 3 includes a generator-side inverter 31 , a grid-side inverter 32 and one of the DC intermediate circuit arranged therebetween 30 ( please refer 2 ). The inverter 3 can be arranged at any point of the wind turbine, for example in the nacelle 11 together with the generator 14 or detached from the nacelle ("gondelfern"), as in the embodiment discussed here. Here is the inverter 3 with the generator 14 over a connecting line 15 connected by the gondola 11 starting through the entire tower 10 down to the connection to the inverter 3 , About one to the grid-side inverter 32 connected connection cable 16 will be the one from the generator 14 generated and from the inverter 3 finally converted electrical power to a network 99 issued.

The basic structure of the inverter 3 is, as is well known, in 2 shown in simplified form. The inverter 3 includes the generator side inverter shown on the left side 31 and the right side grid side inverter 32 , They are linked by a DC voltage intermediate circuit 30 , This has a storage capacity, which in the illustrated embodiment as two series-connected capacitors 34 is executed. DC link side are at the generator-side inverter 31 as well as on the grid-side inverter 32 one smoothing capacitor each 38 intended.

The grid-side inverter 32 has three parallel phase strings, each with two series current valves 36 comprise, at the middle node each one of the phases is connected via a filter impedance 37 , These flow valves 36 in the three phase strands (not shown) signal lines are controlled, the corresponding control signals as A1, A2 and A3 for the three phases of the network-side inverter 32 are designated.

Accordingly, the generator-side inverter 31 also three parallel phase strands, each also two series-connected current valves 35 comprise, at the middle node each one of the phases is connected via a filter impedance 38 , These flow valves 35 are also driven via (not shown) signal lines, the corresponding control signals as B1, B2 and B3 for the three phases of the generator-side inverter 31 are designated.

The control signals A1, A2 and A3 as well as B1, B2 and B3 are from a for controlling the inverter 3 used pulse width modulator 4 provided (see 4 ). In one basic block each 41 . 42 For each of the three phases, a switching frequency is generated. Their frequency and amplitude depends on one by means of the operation control 2 for each of the two inverters 31 . 32 generated control signal. It is generated for the three phases with different phase offset, namely offset by 120 °. In order to enable a digital further processing, the thus frequency-matched and phase-shifted signals are each supplied to a Abtasthalteglied and then from the basic block 41 . 42 output. These signals are referred to as Aref1, Aref2 and Aref3 and Bref1, Bref2 and Bref3, respectively.

These signals are applied to an input of an offset unit 43 . 44 , At the other input, an offset signal Aoffs and Boffs is respectively applied, as will be explained in more detail later. The signals thus generated are referred to as ASref1, ASref2 and ASref3 and BSref1, BSref2 and BSref3, respectively. They are applied to an input of a cycle valve 6 designed to shift at least one of the signals cyclically with respect to the other signals. The output signals of the cycle slide 6 are accordingly referred to as ASShift1, ASShift2 and ASShift3 or BSShift1, BSShift2 and BSShift3.

The control signals thus obtained are applied to a modulation stage 9 and become one of a modulation source there 90 provided carrier signal (in the illustrated embodiment, 2 kHz) modulated. The actual modulation levels are indicated by the reference numeral 91 . 92 designated. They each output a complementary pair of output signals, with each pair connected to the two series current valves in the phase strings of the inverter 3 is created as a control signal.

Provided according to the invention are a cycle position detector 5 as well as the already mentioned cycle slide 6 , The cycle position detector 5 includes a phase sorter 7 as well as a cross comparison unit 8th , Further, a selector 65 for the cycle slide 6 intended.

For a more detailed explanation of the phase sorter 7 and the cross comparison unit 8th will be on the 5 and 6 directed. The phase sorter 7 is designed to sort the drive signals for the three phases according to their size. The three signals are thus resorted so as to determine the one with the smallest amplitude Amin or Bmin, that with a medium amplitude Amid or Bmid and the one with the greatest amplitude Amax or Bmax. For determining the signals with the smallest amplitude and for determining the signals with the largest amplitude are each a minimum generator 71 or a maximum creator 72 intended. The three original signals are applied to their inputs, and the smallest or largest are output at their outputs. The structure of such a minimum generator and maximum generator is known per se and therefore needs in the present case not to be explained in detail. Below is an example of the branch with the network-side inverter A, the structure of that unit 73 which identifies the mid-size amide signal. This unit 73 has a summation element at its input 74 on whose inputs the minimum and maximum signal Amin or Amax determined by the minimum generator or maximum generator are applied. The output of the summation element 74 is applied to an inverter 75 its output in turn to an input of a summation element 76 is created. That's the value of the mid-size amid signal.

Further, the output of the inverter 75 applied to a multiplier 77 which performs a multiplication with the value 0.5. This forms an offset signal Aoffs.

The output of the multiplier is at the other input of the second summation element 76 created. By summation, the corrected by the offset value output signal for the mean value ASmid is formed. Corresponding further second summation elements 76 ' . 76 " are also provided for the signals for the smallest and largest signal Amin, Amax, so that in this way taking into account the offset signal signals ASmin, ASmax are formed. - For the three control signals of the generator-side inverter 32 a corresponding signal processing is provided. It generates the corresponding signal trio BSmin, BSmid and BSmax for the generator-side inverter 32 ,

The two signal trios ASmin, ASmid, ASmax or BSmin, BSmid and BSmax for controlling the network-side or generator-side inverter 31 . 32 are applied to an input of the cross comparison unit 8th , The cross comparison unit 8th is designed to check to what extent the average value of the ONE signal trio lies within the interval spanned by the minimum value and maximum value of the respective OTHER signal trio. Functionally, the cross comparison unit comprises 8th thus an interval former on the one hand and a unit for checking the overlap on the other. Structure and mode of operation of the cross comparison unit 8th will now be with reference to 6 explained. The cross comparison unit has two branches with three inputs each. Below is the branch for controlling the generator-side inverter 32 for generating the BShift signal.

The signals BSmin and BSmax are each applied to a negative input of a differential element 81 . 82 at the entrance of the branch of the cross comparison unit 8th created. At the other, positive input of the differential element 81 . 82 the average value of the other signal trio is connected, ie the average value belonging to the other inverter. This forms an interval formation module. In the present case, this was the signal ASmid. The difference between the comparison between ASmid and BSmax is applied to a limiting module 83 which limits to positive values. The output signal of the limiting module 83 is applied to a first input of a third summation element 85 , The difference between the comparison between ASmid and BSmin is applied to a limiting module 84 , which limits to negative values. The output signal of the limiting module 84 is applied to a third input of the third summation element 85 , The sum of these two values forms the third summation term 85 the value BSshift for the displacement of the control signal for the generator-side inverter 32 , The Elements 83 . 84 . 85 act as a coverage module and work together to check that the value ASmid falls within the interval defined by BSmin and BSmax. If this is not the case, the signal BSshift is generated. This signal is applied to a shutdown element 86 which can suppress displacement if necessary. - The branch for the grid-side inverter is on the right in 6 represented and constructed accordingly. Reference is made to the above explanation, which is applicable here accordingly.

This transition from the three numbered control signals A1ref, A2ref, A3ref to the amplitude-sized signal Amax, amine, amide and, correspondingly, from the signals Bref1, Bref2, Bref3 to Bmax, Bmin, Bmid are in 8th illustrated. The solid line (A) represents the switching cycles of the grid-side inverter 31 The long-dashed line (B) shows the switching cycles of the generator-side inverter. The resorting is done by the phase sorter 7 , Based on its resorting to maximum, minimum and mid-signal, the cross-comparison unit operates 8th , It checks whether the bmid falls within the interval spanned by the maximum values Amin, Amax - that's how 8th shows, the case. It also checks whether the signal Amid is in the interval spanned by the maximum values Bmin, Bmax (see the horizontal curly bracket at the bottom of the image 8th ). This is also the case here. Thus, the relative cycle position of the control of the two inverters is compared. If the situation were such that the signal amid did not fall within the interval between Bmin and Bmax, then the control would be unfavorable. It would then be so amide either left or right of the horizontal brace. The cross comparison unit 8th would then be a displacement signal for the control of the generator-side inverter 32 which would shift all values of B (ie Bmin, Bmax and Bmid) to such an extent that Amide falls into the now shifted interval and thus coverage is established.

Thus, the cross-comparison unit forms 8th based on the two signal trios a shift value, which is the input signal for the cycle shifter 6 serves. In each case, a shift value for the generator-side inverter 32 and for the grid-side inverter 31 educated. However, usually only one signal is used. Which one is used is through the selector 65 certain. This checks the voltage level of the two inverters 31, 32 and passes the displacement signal to the one with the lower voltage. Basically, the selector 65 be executed as a separate entity. However, it has proven itself to him with the cross comparison unit 8th to execute integrated. This is the case in the present case. Due to the one-sided limitation to positive are negative values in the delimiters 83 . 84 is achieved that a shift signal can only arise if the affected branch is that of the inverter with the lower voltage. That way is the selector 65 in the cross comparison unit 8th integrated.

The basic features of controlling the inverter 3 by means of according to 4 . 5 and 6 generated signals are in the 3 and 7 shown. 3 shows the basics on the example of a pulse width modulation for one phase. The triangular wave shown at the top is that of the carrier signal. This is modulated depending on the control signal represented by dashed line. The resulting switching frequency clocks are shown with the two lines below the triangle wave. They show the switching state of the two flow valves in a phase branch, the upper line for the upper flow valve and the lower line for the lower flow control valves (cf. 2 ) stands. The voltage which then sets at the output for the corresponding phase is shown in the lowest line. It can be seen that with increasing control voltage, the width of the pulse for the turn-on signal I increases. This is the concept of pulse width modulation.

It will now be referred to 8th , It shows in its upper diagrams values for a usual in control of the inverters 31 . 32 without phase shift according to the invention. The graph a) shows values for ASref1 (solid line), ASref2 (long dashed line) and ASref3 (short dashed line). The diagram b) shows corresponding values for BSref1 (solid line), BSref2 (long dashed line) and BSref3 (short dashed line). Diagram c) shows the common-mode voltage Acm for the grid-side inverter 31 (solid line) and Bcm for the generator-side inverter 32 (dashed line). The common mode differential voltage Acm - Bcm resulting from different switching cycles are shown in diagram d). One recognizes a multiplicity of sharp spikes, which reach voltages up to +/- 800 V.

Using the cycle shift according to the invention, the cycle position at which the inverters change 31 . 32 be controlled. The resulting common mode voltage Acm for the grid-side inverter 31 (solid line) and Bcm for the generator-side inverter 32 (dashed line) are shown in diagram e). The differences may seem small at first glance. However, if one considers the difference between the two more exactly, as shown in diagram f), it becomes clear that a considerable reduction could now be achieved. It should be noted that the diagram f) is scaled differently. It can be seen that the differential common-mode voltage now barely reaches +/- 400 V, that is to say only half compared to the scenario shown in diagram c), d) without the invention. A halving of the voltage leads to a power reduction of interference due to the common-mode voltages to a quarter of the output value. That's a considerable reduction.

Reference is now made to the 9 It shows two different situations in the left and right half of the picture. The left half of the figure shows an operation of the generator-side inverter 32 with a lower voltage than that of the grid-side inverter 31 , In the right half of the screen, on the other hand, the generator-side inverter has a higher voltage (and frequency). Diagram a) shows values for ASref1 (solid line), ASref2 (dot-dashed line) and ASref3 (dashed line). Diagram b) shows the phases now broken down into the largest ASmax (dot-dashed line), the middle ASmid (solid line) and the smallest ASmin (dashed line). Diagram c) shows the original values for BSref1 (solid line), BSref2 (long dashed line) and BSref3 (short dashed line). The diagram d), in turn, shows the phases broken down by their size, namely BSmax (dot-dashed line), the middle BSmid (solid line) and the smallest BSmin (dashed line). The one of the cross comparison unit 8th calculated value for the phase shift is in the in the diagram e) for the grid-side inverter 31 and f) for the generator-side inverter 32 shown. Since in the left half of the picture, the grid-side inverter 31 which has greater voltage, its values are not shifted. There is therefore no shift signal for him. The shift signal applies only to the generator-side inverter 32 as shown in diagram f).

This is different for the other operating case, which is shown in the right half of the picture. Here is the voltage of the generator-side inverter 32 the bigger one. Accordingly, its signal is not shifted, but instead the shift occurs in the grid-side inverter, as shown in diagram e).

Thus, with a minimum of interference in the inverter control, the invention achieves a significant reduction in common mode voltage, and in particular, the resulting power density for noise. The invention is particularly suitable for the arrangement in wind turbines, which have widely spaced generators and converters; but it is also suitable for the joint arrangement of generator and inverter. Since only modifications in the inverter control are required, the invention is particularly suitable for retrofitting existing wind turbines.

Claims (17)

A wind turbine comprising a generator (14) in a nacelle (11) driven by a wind rotor (12) and an inverter (3) cooperating with the generator (14) for generating electrical power from a connection line (15) between Generator (14) in the nacelle (11) and the inverter (3), wherein the inverter (3) comprises a mains side and a generator side inverter (31, 32) whose flow valves (35, 36) are cyclically controlled by means of a switching frequency, characterized in that there is further provided a synchronous with both inverters (31, 32) carrier for controlling the flow control valves (35, 36) each having a cycle position, a relative position detector (5) which is adapted to the cycle position for both inverters (31, 32) to determine and determine their relative position to each other, and a Zyklenlageschieber (6), which cooperates with the relative position detector (5) and is designed to shift the cycle position at least one s the inverter (31, 32) depending on the determined relative position. Wind turbine after Claim 1 , characterized in that the converter (3) is arranged remote gondel at the wind turbine. Wind turbine after Claim 1 or 2 , characterized in that the relative position detector (5) is adapted to control the cycle shim (6) only when the relative position is outside of an interval. Wind turbine after Claim 3 , characterized in that limits of the interval are dynamic. Wind energy plant according to one of the preceding claims, characterized in that there is further provided a selector (65) which determines one of the two inverters (31, 32) on which the cycle bearing slide (6) acts. Wind turbine after Claim 5 , characterized in that the selector (65) is load-controlled, preferably designed to select the inverter (31, 32) with the lower load dimension, wherein the voltage and / or the duration of the interval preferably acts as the load measure. Wind energy plant according to one of the preceding claims, characterized in that the relative position detector (5) has a phase sorting unit (6) which is preferably designed to sort the phases of the inverters (31, 32) according to their amplitude. Wind energy plant according to one of the preceding claims, characterized in that the relative position detector (5) comprises a cross-comparison unit (7) which is adapted to cross-compare the phases of the inverters (31, 32). Wind turbine after Claim 7 and 8th , characterized in that there is further provided an interval forming module (81, 82) which determines an interval from a minimum and a maximum phase of the inverter. Wind turbine after Claim 9 , characterized in that there is further provided a coverage module (82, 84, 85) adapted to check whether a mean phase value of one of the two inverters is in the interval of the other of the two inverters. Wind turbine after one of the Claims 8 to 10 , characterized in that the cross comparison unit (7) and the selector (65) are combined with each other. Wind energy plant according to one of the preceding claims, characterized in that the cycle bearing slide (6) is arranged in the signal travel direction in front of a pulse width modulator (4) of the flow control valves. Inverter for retrofitting a wind turbine with a generator (14) in a nacelle (11) driven by a wind rotor (12), the inverter being connected to the generator (14) cooperates to generate electrical power, wherein the inverter (3) comprises a network-side and a generator-side inverter (31, 32) whose flow valves (35, 36) are cyclically controlled by means of a switching frequency, characterized in that further provided with a one with two inverters (31, 32) synchronous carrier for controlling the flow control valves (35, 36) each having a cycle position, a relative position detector (5) which is adapted to determine the cycle position for both inverters (31, 32) and their relative position to determine each other, and a Zyklenlageschieber (6) which cooperates with the relative position detector (5) and is adapted to shift the cycle position of at least one of the inverters (31, 32) depending on the determined relative position. Inverter after Claim 13 , characterized in that it according to one of Claims 2 to 12 is further developed. A method of operating a wind turbine comprising a generator in a nacelle driven by a wind rotor, a converter cooperating with the generator to generate electrical power, and a connection line between generator in the nacelle and the inverter, the inverter having a generator side and a network-side inverter with flow control valves, whose flow valves are cyclically controlled at a switching frequency, characterized by synchronously controlling the flow control valves of both inverters, each with a cycle position, detecting a relative position include determining the cycle position of both inverters and determining a relative position of the cycle layers, and shifting the cycle position of one of the inverters depending on the determined relative position. Method according to Claim 15 , characterized by shifting only the cycle position of the inverter with lower voltage. Method according to Claim 15 characterized by operating the inverter according to one of Claims 1 to 11

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